[omm][temporarily breaking] Bank relationships and some storage iface

[Dcallies]

Summary

This PR:

1. Does some more work on the bank data model, which should flex it out to allow bank -> content -> hashes
2. Rewrites some of the sqlalchemy in whatever the heck the mainline docs use: https://flask-sqlalchemy.palletsprojects.com/en/3.1.x/quickstart/ and https://docs.sqlalchemy.org/en/20/orm/basic_relationships.html#one-to-many
3. Breaks the existing curation API while I continue tooling on it

As part of this, I couldn't figure out a way to make both sqlalchemy and dataclasses happy at the same time, so we're doing something immensely stupid and just translating between them.

Test Plan

mypy